JPS61142495A - X-ray absorption filter for x-ray computed tomographic device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray absorption filter for X-ray CT equipment, and more particularly to an X-ray absorption filter that reduces the dynamic range of the intensity of transmitted X-rays from a patient.

(Prior Art) In an XIICT device, the intensity ratio of X-rays that reach the detector is as high as 1:1000 to 2000 between the part that passes through the patient and the part that does not pass through the patient.

Such a large dynamic range places a heavy burden on the linearity of the sensitivity of the detector itself and on the processing circuit that processes the detection signal.

Therefore, as a conventional method for reducing the dynamic range of the Xl1l CT apparatus, an X-ray absorption filter is used as shown in FIG. In this figure, 1 is x
xsii tube that emits m, 2 is an X-ray absorption filter, a
is the patient and 4 is the detector.

Here, the XS absorption filter 2 is made of organic glass.

It is made of solid material such as Teflon or aluminum, and has a structure that has a transmittance increase/decrease characteristic opposite to that of the patient with respect to a fan beam angle of xm. Such an X-ray absorption filter 2 is used in a specialized manner depending on the imaging unit of the patient. For example, a head with a small imaging area (approximately 20CIIl in diameter) and a large abdomen (approximately 40CIIl in diameter)
It is difficult to share one type of filter shape with
The m-absorption filter is mechanically switched and used.

FIG. 5 is an explanatory diagram of a conventional xw4 absorption filter.

Here, (a) in FIG. 5 shows the one for the abdomen, and (b) shows the one for the head. The shape of conventional XS absorption filters is similar to the back projection of the patient as a cylindrical body of water, with gentle curves for abdominal filters and steep curves for head filters. ing.

(Problem that the invention aims to solve) However, the size of the imaging area of the patient varies depending on the patient, and two types of specialized X-ray absorption filters cannot sufficiently reduce the dynamic range of transmitted X-ray intensity. Furthermore, there were other problems such as requiring a mechanically complex drive mechanism including a motor for switching the X-ray absorption filter.

The present invention has been made in view of these points, and its object is to provide an X-ray absorption filter having a type 111 shape and capable of changing the dynamic range of the transmitted XwA intensity in an analog manner.

(Means for Solving the Problems) The present invention, which solves the above problems, is an X-ray absorption filter for reducing the dynamic range of the transmitted X-ray intensity. It is a hollow pressure-tight airtight container with a shape similar to the back projection of the inside of the container, and the interior is filled with a gas that has low transparency to X-rays, and it is configured so that the xm iron absorption characteristics can be changed by changing the gas pressure. This is a characteristic feature.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1(A) is a main part configuration diagram showing an embodiment of the xm absorption filter of the present invention, and FIG. 1(B) is a sectional view taken along line AA' of the filter of FIG. 1(A). In this figure, 10 is an X-ray absorption filter similar to a conventional filter, which is close to the back projection of the depth in the fan beam angle direction when the patient is regarded as a cylindrical body of water. This xw4 absorption filter 10
The upper and lower parts 13 and 14 are made of aluminum alloy, beryllium material, etc. with good X-ray transmittance, and the side plates 11°1
2 is a hollow pressure-resistant container formed of an end plate that does not transmit X-rays. Furthermore, the surfaces 13 and 14 that transmit X-rays are thin. In particular, the central portion, where X-ray absorption must be minimized, is thin. 20 is a tank containing Xe gas with good XI transmittance to be put into the X-ray absorption filter.
Gas is sealed into the X-ray absorption filter 10 via a pipe 30 and a pump 40.

The lower surface of the xII absorption filter 10 is gently curved to match the abdomen of a patient's standard body shape.

A gas pressure of about 4 k is generated in such an X-ray absorption filter 10.
Xe gas is filled with the pump 40 so that the ratio is Q/cs2. The gas pressure can be changed arbitrarily using the pump 40.

The XII absorption rate at this time can be expressed by the following formula.

! / r o = e-PJ”P where Io is Xla incident intensity, I is X-ray transmitted intensity, μ
is the XS absorption coefficient, ρ is the specific gravity of the gas, l is the depth in the gas, P is the gas pressure, and μ and ρ are constants specific to the sealed gas.

For a patient's abdomen and head at a certain fan beam angle θ, it is necessary to increase the Xs absorption amount of the latter compared to the former. In conventional filters, both the head and abdominal filters were prepared and the amount of X-ray absorption was changed in two stages by mechanically switching between them. However, in the present invention, by changing the gas pressure P, Change the amount of absorption. Further, in the present invention, since the gas pressure can be adjusted arbitrarily, detailed settings can be made according to the patient's body shape.

Now, set the abdominal gas pressure P of the x-ray absorption filter 10 to about 4
If it is ko/cs2, it can be achieved at about 9 kg/c*2 for the head, making it possible to create an X-ray absorption filter that obtains an appropriate amount of X-ray absorption.

In addition, by using a solid solid filter as part of the filter, Xl! can be achieved at low gas pressure! It is also possible to adopt a configuration in which the amount of absorption is changed.

FIG. 3 is an explanatory diagram showing such a structure.

In this figure, the shaded area 60 is a solid solid filter for the abdomen, and the outer diameter 50 of the X-ray absorption filter is the same as the outer diameter of the solid solid filter for the head.

This container 70 is a hollow gas chamber.

xI configured like this! In the absorption filter,
When the hollow gas chamber 70 is not filled with gas, it is used for the abdomen, and when Xe gas is filled in the hollow at a gas pressure of about 4 kg/C1, it is used for the head. That is, when the internal gas pressure of the hollow gas chamber is Q kg/cm2, it is for abdominal use, and it is about 4 ka/c.
If it is set to 1, an XIIA absorption filter for the head can be achieved,
The amount of X-ray absorption can be changed more efficiently.

In this case, the hollow chamber may be filled with a liquid whose density has been adjusted instead of the Xe gas.

(Effects of the Invention) As explained above, according to the present invention, unlike the method of mechanically switching the X-ray absorption filter as a method of reducing the dynamic range of the transmitted X-ray intensity of the xmcT device, the By placing an X-ray absorbing gas in a hollow container and changing the gas pressure, the X-ray filter absorption characteristics (transmission xwA intensity characteristics and transmission XI! energy spectrum characteristics) can be changed in an analog manner. , 1 ton of X-ray absorption according to the shape of the patient
s! 1 is obtained. Further, by filling the hollow container with a solution having an arbitrary density or average atomic number, the filter absorption characteristics can be changed in the same way.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of main parts showing an embodiment of the XI absorption filter of the present invention, Fig. 2 is an explanatory diagram illustrating the fan beam angle and depth within the gas, and Fig. 3 is an illustration of the X-ray absorption filter of the present invention. FIGS. 4 and 5 are main part configuration diagrams showing other embodiments, and FIGS. 4 and 5 are main part configuration diagrams showing a conventional X-ray absorption filter. 10... X-ray absorption filter 20... Tank 30... Vibrator 40...
Pump 60...Abdominal solid filter 70...Hollow gas chamber Patent applicant Yokogawa Medical Systems Corporation (HEM)

Claims (1)

[Claims] X to reduce the dynamic range of X-ray transmission intensity
This is a radiation-absorbing filter, which is a hollow, pressure-resistant sealed container with a shape similar to the back projection of a patient as a cylindrical body of water.The inside is filled with a gas that has low transparency to X-rays, and the gas pressure is changed. An X-ray absorption filter for an X-ray CT apparatus, characterized in that the X-ray absorption filter is configured such that the X-ray absorption characteristics can be changed by changing the X-ray absorption characteristics.